Don't take this the wrong way. No dis-respect.
You can even top those figures by using a motorcycle. But you will be sacrificing convenience. A person whose car is doing 14 KM/L might be travelling in more safety and comfort than your 27 KM/L limit. You are basically paying for convenience.
And these comparisons are fair for same class of vehicles with same level of service. If comfort and convenience hold little value to you then motor cycle is the best option. Even if you have to make the trip two times to haul everyone.
If a JDM on petrol can top the mileage of a CNG car then if will be a remarkable feat no doubt. But basically you are comparing a cramped car with a roomy one, a car with kamani with a car with shocks; a car with working AC with a car where you have to compromise on AC cooling; a car with power steering, power windows, more powerful engine output, more comfortable, most probably an automatic with a car that in my opinion is basically prime example of why democracy has never worked properly in this country.
A JDM dinky will outdo Mehran on most fronts, but achieving more fuel economy due to less price of CNG by sacrificing comfort, convenience and safety is not one of them yet.